This invention relates generally to an impedance converter, and more specifically to a maximum power tracker for use with current limited power supplies.
In matching a power supply to a load, it is conventional to have some form of transformer or impedance converter to optimize the match as either load or source changes. The impedance conversion is usually done with a view toward maximizing the power supplied by the source and made available to the load. One such maximum power tracker operates by sensing the voltage and current at either the load or source, recording the power, then moving the operating point a small amount and comparing the power at the new setting with the previous value. If the power measured at the new setting is larger, the operating point is moved again, in the same direction, and a new comparison is made. This process is repeated until the power value at the newest operating point is lower than the immediately previous value. The operating point is then moved in the opposite direction until the power drops again. There is thus a continued "hunting" of the operating point, even if both source and load are constant, as the logic within the power tracker hunts for the optimum operating point. This type of power tracker or impedance converter requires A/D conversion, multiplication, memory, comparison logic, and current and voltage sensors. The necessity for all of these components dictates an expensive and complicated system.
Regardless of the expense, however, there is a very serious need for power trackers. One example in which a maximum power tracker is very necessary is the running of electric motors such as in water pumping from deep wells with volumetric pumps using a photovoltaic array as a power source. Early in the day when the solar energy available to the array is low, and thus the current from the array is also low, there may not be enough current available, in the absence of some matching between load and source, to start the motor. Accordingly, some impedance matching is necessary which maintains the array near its maximum power output point and yet satisfies the drive needs of the motor. As the sun rises and the energy available to the array increases, thereby increasing the current supplied by the array, the power tracker should maintain the array at or near its maximum power output point.
A need therefore existed for an impedance transformer which would maintain the power source at or near its maximum power output while avoiding the expense, problems, and complexity of the prior art solutions.
It is therefore an object of this invention to provide an improved impedance converter which will maintain a power supply, over its useful operating range, at or near its maximum power output.
It is another object of this invention to provide an improved power tracker for use with a current limited power supply.
It is a further object of this invention to provide an improved and simplified impedance converter.
It is a still further object of this invention to provide an improved power tracker circuit for use with a photovoltaic array.